Abstract:Pu'er city is located in the Southwest of Yunnan Province.The onset date of summer rainfall is very important for the crop and tea production in Pu'er.Based on the variation of interannual increment of onset date of Pu'er rainy season and the atmospheric circulation and physical process affecting the onset date of the rainy season,five key predictors with physical significance are selected by using the year-to-year increment approach.The five predictors are the circumpolar circulation in the Southern Hemisphere in January,the South Pacific high in February,the sea level pressure from the Bay of Bengal to the South China Sea in April,the sea ice in northern Canada in the previous winter,and the snow depth in Iranian plateau in the previous winter.A prediction model of the onset date of the rainy season in Pu'er is established by using the multiple linear regression analysis method.The cross-validation tests for the period 1967-2017 and the independent hindcast for the period 1998-2017 are performed to validate the prediction model.In the cross-validation test,the correlation coefficient in interannual increment between predicted and observed onset date of the rainy season is 0.84,and the relative root mean square error is 24%.In the independent hindcast,the relative root mean square error of interannual increment of onset date of the rainy season is 15%,and the prediction error of onset date of the rainy season is less than 7 d,showing that the prediction model can well reproduce the change trend of onset date of the rainy season from 1967 to 2017.

Abstract:In this study,based on the 1-7 day precipitation forecasts from the ECMWF,JMA,UKMO and NCEP in the TIGGE dataset and the hourly precipitation data merged by China Automatic Weather Station(CAWS) and CMORPH precipitation products as the observation data,the precipitation forecast in China is calibrated by using the frequency matching method(FMM).First,the Kalman filter was used to improve the statistics of the precipitation frequency.China was divided into seven sub-regions for the FMM calibration of the precipitation forecasts in accordance with its different precipitation intensity in various regions.The results show that FMM can significantly reduce the forecast error of precipitation intensity and area.Overall,FMM can improve the forecast skill of precipitation at different thresholds.After calibration,the ETS score of the precipitation forecast is significantly improved,and the false alarm rate of light rain and the missing rate of heavy rain are considerably reduced.In addition,the forecast skill for "rain or no rain" events is significantly improved.In addition,FMM can bring the forecast rainfall area closer to the observed values,particularly reducing the false alarm rate of light rain in a vast area.FMM can only improve the intensity and scope of the precipitation by means of adjusting the amount of rainfall.However,the location and shape of the heavy rainfall area cannot be improved.

Abstract:In this study,using daily data from the NCEP/NCAR reanalysis dataset and precipitation observations recorded at 574 stations,two heavy rainfall processes during the periods of June 7-11 and 18-22,2010 occurring in the middle and lower reaches of the Yangtze River(MLRYR) are compared based on their respective circulations,Rossby wave activity fluxes,and tropical convection activities.The results show that a downstream propagation Rossby wave and double-block high were present in the mid-high latitudes throughout the time when these two processes occurred.During these events,it is shown that the intensity of the western Pacific subtropical high(WPSH) was stronger and the western extension point was more westward than normal in the low latitudes.However,two major differences are observed between the events:1)The source of the Rossby wave was located in northern Europe.Due to a low-pressure trough over the Lake Baikal area,the cold air turned southward to about 36°N.At the same time,the strengthened and westward WPSH were located at about 95°E.Next,the cold and warm air converged,leading to heavy rainfall.2)The source of the Rossby wave was located in northern Europe and central Siberia.The low-pressure trough in East Asia was more prominent than in the first rainfall process,which was conducive to the cold air reaching the MLRYR(about 30°N).In addition,the westward extension of the WPSH was located at about 90°E.The cold and warm air converged in the MLRYR and in its southern area,thereby leading to heavy precipitation in these regions.

Abstract:Based on the National Centers for Environmental Prediction-Department of Energy(NCEP-DOE) Atmospheric Model Intercomparison Project Phase-Ⅱ(AMIP-Ⅱ) reanalysis data,the sea surface temperature data of Hadley Center and the observed rainfall data of 160 stations in China during 1979-2014,this paper investigated variation of summer Atlantic Niño and its association with summer rainfall anomaly in China by using the empirical orthogonal function(EOF) analysis and regression analysis methods.Results suggest that the summer Atlantic Niño is the first EOF mode of SST anomalies in the tropical Atlantic Ocean,with a variance contribution rate of 33.7% and an obvious interannual variation.When the Atlantic Niño is in the warm phase in summer,there is an obvious anomalous anticyclone in the lower troposphere over the western North Pacific.Under the influence of the anticyclone,the western Pacific subtropical high enhances and extends westward,and the southwest wind anomaly appears in South China,which is conducive to the water vapor transport from the Southwest side of the western Pacific subtropical high to the Yangtze River Basin and its north area,so the precipitation in the Yangtze River Basin and North China increases,while the southeast coastal area of China is controlled by the anomalous anticyclone over the western North Pacific,which is not conducive to the occurrence of precipitation,and vice versa.

Abstract:The Global Precipitation Mesaurement (GPM) satellite provides the next generation of global satellite precipitation products.We selected the super typhoon "Maria" (201808),which occurred in July 2018,for study in this paper.We analyzed the precipitation rate,the type of precipitation and height of the rain top,variation of the vertical profile of the precipitation rate,and distribution characteristics of the three-dimensional structure of the precipitation rate at two different times.The following main conclusions are drawn:At both times,Maria was in the super typhoon stage,and the eye area of the typhoon was a deep convection area at time A,while at time B the convection in the eye area was weakened,yet a strong spiral rain belt was present.The maximum precipitation rate did not correspond to the height of the storm top at both times A and B,nor did it correspond to the microphysical processes in the precipitation cloud system.The high value region of water particle content detected by a low frequency GMI of 18.7 GHz corresponds closely to the heavy precipitation rate.In addition,the signal of ice particles detected at a high frequency of 183.31±3 GHz was consistent with the distribution of the height of the storm top.The vertical profiles corresponding to different precipitation rates showed that the precipitation rate changed sharply at a 5 km altitude,which was due to either the collision and growth of raindrops or the decrease of evaporation at this altitude.From time A to time B,the radius of cloud wall greater than 10 mm·h^-1 decreased significantly.There were weak precipitation areas present,and no precipitation areas were observed between the eye wall and spiral rain belt at time B.

Abstract:An anti-phase relationship of precipitation anomaly between first and second rainy seasons is analyzed based on the daily precipitation data of 134 stations in Guangdong Province and Guangxi Zhuang Autonomous Region (hereinafter Guangdong-Guangxi region) at a total of 2 400 surface meteorological stations of China,the monthly sea surface temperature data from the Hadley Center in the UK,and the monthly NCEP/NCAR reanalysis data from 1961 to 2018.This paper selected those years when the precipitation is above/below-normal in first rainy season (April-June) and below/above-normal in second rainy season (July-September) in the Guangdong-Guangdong region.Results show that in the past 60 years,the anti-phase relationship of precipitation anomaly between first and second rainy seasons in Guangdong-Guangxi region is closely related to sea surface temperature (SST) anomaly in the tropical western Pacific.During the first rainy season,when SST anomalies in the tropical western Pacific are negative,the Rossby wave response of the atmosphere to the negative SST anomalies causes an anomalous anticyclone circulation in the western North Pacific.The water vapor is transported and converged from the tropical western Pacific to Guangdong-Guangxi region.Guangdong-Guangxi region is the wet advection area of water vapor and the anomalous convergence area of wind.The anomalous ascending motion of air is dominant in Guangdong-Guangxi region.This circulation configuration is conducive to the positive precipitation anomaly during the first rainy season.The negative SST anomalies in the tropical western Pacific can persist to the second rainy season.The cold source of the heating could also cause an anomalous anticyclone in the western North Pacific through Mastuno-Gill response,but the location of the anticyclone is more northwestward in the second rainy season than that in the first rainy season.The water vapor anomalies are divergent in Guangdong-Guangxi region.Guangdong-Guangxi region is the dry advection area of water vapor and the anomalous divergence area of wind,and is also controlled by the anomalous descending motion.Above circulation configuration is not conducive to the precipitation in Guangdong-Guangxi region.When SST anomalies in the tropical western Pacific are positive,the above situations are opposite.

Abstract:In this study,based on the European Centre for Medium-Range Weather Forecasts (ECMWF) of 2 m surface air temperature and automatic weather observatory data of China,the correlation among the initial field bias,historical bias,Kalman filter predicted bias the real-time bias is analyzed.Four daily maximum and minimum temperature forecast regression schemes are designed.A comparison among ECMWF,CMA and provincial forecasting is investigated.The results show that the improved scheme's predicted temperature,historical bias,initial field bias and Kalman filter inversion bias as the predictor are all optimal.In addition,the scheme's forecast quality for the maximum and minimum temperatures in 2017 is significantly better than that of both ECMWF and CMA,particularly in areas featuring complex terrain.Compared with the best-performing provincial forecasting,the maximum temperature MAE is 8.24%~13.97% lower than the provincial forecast,while the forecast accuracy is increased by 1.24%~3.57%,and the daily minimum temperature MAE is 9.43%~17.69% lower than the provincial ones.The forecast accuracy rate increased by 1.77%~2.72%.Additionally,it shows the greatest improvement within 1 day,thus indicating that the correction effect decreases considerably with the forecast lead time.

Abstract:Temperature changes in the Arctic lower stratosphere on both the short-and long-term timescales are critical for changing the magnitude of ozone losses in the Arctic vortex.In the present paper,first we give an approximate thermodynamic equation,which is in the form of that described by Hu and Tung (2002),for diagnosing the polar stratospheric temperature changes,along with its time-sliding calculation scheme.Next,according to this scheme and using the MERRA-2 reanalysis daily data for the period of 1980-2000,we calculate the terms of monthly temperature increment,dynamical heating and diabatic heating,as well as their respective linear trends,at 100 hPa in the Arctic lower stratosphere.The results show that the monthly temperature increment term and sum of the cumulative dynamical and diabatic heating,as well as their trends,are approximately balanced during the annual cycle of climatological average.Then,based on a multivariate linear regression,we further obtain the respective contributions of the dynamical and diabatic heating to the current month temperature trends.It is shown that the dynamical contribution to the temperature trend is dominant and varied with the different months in the Arctic lower stratosphere wintertime,while the diabatic contribution is dominant in other seasons.This is particularly pertinent to the attribution of decadal scale Arctic stratospheric temperature changes,due to the internal dynamics variability and anthropogenic climate forcings.In future work,it would be desirable to determine the reasonable range of the eddy heat flux approximation with regard to the reference latitude,pressure height and integration timescale,as well as to disclose more application aspects of the simplified thermodynamic energy equation.An assessment for the relative impact of each deviation factor is also required to obtain an accurate explanation for sources of some large departures and limits of the approximate temperature change equation.Of course,verifications and comparisons using greater numbers of and more varied data sets are required.

Abstract:Based on the NCEP/NCAR reanalysis data I,the differences in frequency,intensity and related circulation patterns of stratospheric sudden warmings(SSWs) during the past 68 years(1948-2015) were compared.The statistical results showed that 30 SSWs occurred from 1948 to 2015 mainly in cold months from November to March.SSWs occurred more frequently in January and February than in other cold months.In addition,the frequency of SSWs was different from decade to decade.The composite results showed that SSWs in November and December lasted for a longer time than those during January and March.SSWs in March were much weaker and lasted for a shorter period than those in other cold months.The parallel comparison results indicated that the zonal mean signals associated with SSWs in January and March extended downward deeper than those in November,December,and February.The zonal mean signals in November,December,and February could only reach 200 hPa.A negative Western Pacific(WP) pattern was observed one or two weeks before SSWs in all cold months.However,a positive Pacific-North America(PNA) pattern only appeared before SSWs in November,December,and March.Moreover,a negative North Atlantic Oscillation(NAO) pattern was observed one or two weeks after SSWs in November,January,and March.

Abstract:In this study,based on the reanalysis data of NCEP/NCAR and NOAA SST data,the relationship between the anomaly of air-sea coupling in the Northern Hemisphere and the synergistic change of storm tracks in the interdecadal background of different PDO phases is analyzed.The results are summarized as follows:1) It is shown that a significant correlation is present between the interdecadal oscillation of the Pacific Ocean and the synergistic variations of the storm tracks over the Northern Hemisphere in winter.When PDO is in warm phase,it corresponds to the anomalous variation of the northern and southern positions of the two oceanic storm tracks.Additionally,the North Pacific storm tracks are southerly,and the central and eastern parts are weakened,while the North Atlantic storm tracks are enhanced in the north-central part of the north.The current variations of the two storm tracks are opposite when PDO is in cold phase.2) When PDO is in warm phase,it corresponds to the El Niño SST anomaly,and the North Atlantic SST is tri-polar;in addition,the mean trough ridge is strengthened,the meridional circulation is strengthened,the polar vortex is contracted,the North Pacific storm tracks are southward,while the Atlantic storm tracks are northward.At this time,the temperatures in the northern part of Eurasia and most parts of North America are rise abnormally,while those in southern Asia,northern Africa and the North Barents Sea drop abnormally,as do those in the southwestern part of North America and Greenland.The above situations are opposite when PDO is in cold phase.

Abstract:Based on the statistical analysis of heavy precipitation in southeast coast of China in winter (December,January and February),the European Center winter precipitation data during 2011-2016 were classified by the EOF,REOF and North test methods,and the first and fourth REOF modes located inland were selected.The composite analysis of precipitation samples of the two modes shows that the composite precipitation centers are consistent with the multi-year statistical rainstorm centers in Fujian province.In combination with the heavy rainfall,there is an asymptotic convergence flow from north to south with a front zone at 1 000 hPa,which forms a synoptic scale asymptotic frontogenesis convergence line.The heavy precipitation is usually located on the left side of convergence axis where a cyclonic wind shear exists.This is a type of winter rainstorm system in southeast coast of China that has not been specifically concerned and discussed in the past.The structure of the rainstorm system is confirmed and diagnosed by an objective determination method and establishing a coordinate system of the system.In the cold and dry winter with less rain and prevailing northerly wind at the low level,this kind of system has both the thermal uplift in the front area and the dynamic uplift of convergence air flow,forming a vigorous ascending motion in the rain area.Meanwhile,through the orthogonal wind component of convergence line,the water vapor from adjacent sea surface is collected into the precipitation area,combined the southerly airflow at the west edge of the subtropical high at the middle and upper levels,forming a relatively deep confluence water vapor transport layer.By the non-adiabatic heating,the deep thermal convection instability is formed.Through the dry area wedging under the moisture mass,the wet dynamic instability of the lower dry and upper wet is formed,and the pseudo-equivalent potential temperature decreases with the increase of height,forming a convection instability layer of the upper warm wet and the lower cold dry.Therefore,the system has an important impact on the occurrence and development and the falling area of heavy rainfall in winter.The influence of environmental thermal mechanism is discussed by the simulations of WRF model.Results show that the condensation latent heat heating can affect the convergence position and intensity of the convergence line,the position and intensity of frontogenesis area,and then affect the activity of the system.The latent heat heating in the middle levels can prevent the advection sensible heat cooling into the warm air mass,and maintain the thermal instability and precipitation intensity in the rainfall area.The asymptotic frontogenesis convergence line is conducive to the occurrence of heavy rain in the large-scale precipitation in Fujian in winter,in which the condensation latent heat release plays an important role.

Abstract:The role of data assimilation is to provide a superior initial field for application in numerical models by means of applying observation data.The three-dimensional variation method is widely used in operational forecasting,due to its rather low computational costs and strong assimilation ability.An important component of the three-dimensional variation method is background error covariance,which can directly affect data assimilation and numerical prediction results.Due to the fact that the background error covariance is very substantial,in practical application the analysis increment is often used to solve the minimization problem of the three-dimensional variational cost function.Different control variables have various assimilation and prediction effects,thus selecting appropriate control variables is an important prerequisite for building a reasonable assimilation system.At present,the two most frequently used dynamical control variable schemes are the stream function potential function(ψ-χ) scheme,and horizontal wind components(U-V) scheme.These are considered to be respectively suitable for large-scale assimilation and convective scale assimilation.However,neither the specific characteristics of the two schemes in typhoon scale assimilation nor their impact on typhoon forecasting have yet to be investigated.In this study,based on the WRF-3DVarDA system,we analyze the statistical characteristics of the background error covariance of the two different control variable schemes.Next,we carry out an ideal test of single point observation assimilation and 20 groups of continuous cycle assimilation and prediction experiments in regard to five typhoon events.The analysis results of the background error covariance statistical characteristics of the two schemes show that the background error is smaller and the length scale is larger in the ψ-χ scheme,while more obvious local features and larger variance are found in the U-V scheme.In addition,the results of a single point observation test confirm the statistical characteristics of the two schemes,and also reveals that ψ-χ as a control variable can lead to a false negative increment.The results of batch experiments show that in general the U-V scheme is superior to the ψ-χ scheme,in terms of typhoon track error,maximum wind speed error and minimum sea level pressure error.The diagnostic analysis results show that the greater number of reasonable thermal and dynamic structural features in the U-V scheme are the source of improvement in the typhoon forecast.

Abstract:In this study,based on the routine pollutant monitoring data,satellite data,reanalysis data,backward trajectory models,etc.,the causes and characteristics of a strong dust weather process which occurred in the Beijing-Tianjin-Hebei region in 2017 was analyzed.The study results showed that the synoptic situation of the cold front was what had mainly led to this process,along with the continuous supplement of cold air after the trough.The major sand-dust sources were located in the Badan Jilin Desert and Tengger Desert.Backward trajectory simulation suggested that the contribution to the increasing dust in the Beijing-Tian-Hebei region originated from the northwest.In addition,the cities surrounding the northwest long-distance trajectories suffered from different levels of pollution.The sensible heat flux increased rapidly in the sand-dust sources,which combined with the cold advection in the middle and lower layers,in turn enhancing the unstable stratification and promoting the sediment discharge.The strong,high-level wind speed strengthened and continued to extend downward.The secondary circulation in the middle and low levels developed,which not only transferred and descended the dust particles,but also caused the high momentum and high potential vorticity of the upper level to pass downward.The low-level jet and systems were formed and developed,thereby maintaining the strong wind and dust weather.The negative horizontal helicity had a high correspondence with the occurrence area of dust weather.When the dust weather was passing through,the dust type aerosol appeared between the surface and a height of 4 km.In addition,the concentrations of PM_2.5 and PM₁₀ exhibited high consistence in variation,and led to the level of severe pollution.Furthermore,the values of aerosol optical depth (AOD) and air quality index (AQI) had a high correlation in both the spatial and temporal distributions.The temporal and spatial distributions showed that the value of AOD exceeded 1 during the high pollution period,and dropped below 0.6 when the extent of pollution gradually decreased.

Abstract:In this study,based on the results of WRF model simulation with an NSSL microphysical scheme,which included prediction of cloud condensation nuclei(CCN) concentration and volume of graupel in hail,a hail storm that developed in Nanjing was simulated,and three different CCN initial concentrations were used.The variation of precipitation and hydrometeor,as well as the vertical distribution of the hydrometeor,temperature and wind at different stages of the storm's development,were investigated.The results revealed the following:1)Greater CCN concentration decreases the precipitation during the early stage,yet increases the precipitation during the later stage.2)Greater CCN concentration leads to the enlargement of the high dBZ area(>40 dBz) and the atrophy of the middle dBz area(<40 dBz).3)Greater CCN concentration increases the amount of snow and ice,decreases the graupel,and delays the appearance of the high peak of the hail amount.4)Increased concentration of CCN inhibits rain production,indirectly rendering the helium particles more prone to dry growth,with a lower average density.5)Greater CCN concentration suppresses an early warm cloud process,but promotes the production of snow and ice,which causes the hail storm to be stronger and last for a longer period of time.

Abstract:In this study,the sounding data in the atmospheric boundary layer from 14 December 2016 to 4 January 2017 at the national climate observatory in Shou County,Anhui Province were used in conjunction with the meteorological data from conventional ground stations,pollutant concentration data and synoptic charts,to analyze the accumulation and removal processes of two heavy pollution events in this area.The analysis revealed the following key points.First,both heavy pollution episodes originated under stagnant atmospheric conditions unfavorable for diffusion (such as surface wind speed less than 3 m/s,and high relative humidity of greater than 80%),and were later alleviated by strong wind,precipitation and other favorable conditions for diffusion and deposition.Second,in terms of weather conditions,the high and low stratifications were stable during the accumulation of heavy pollution,and the lower layer was in the wet area,which was mostly controlled by warm tongue or accompanied by warm advection.At the same time,regional transport of pollutants was present.During the first heavy pollution removal,the weather control system in Shou County gradually changed to low pressure,and the lower layer was mostly east wind,with precipitation.The second process was caused by wet deposition of fog and removal of inversion layer.Finally,during the accumulation period of heavy pollution,the boundary layer height was low and the maximum height was only 500 m,which limited the vertical diffusion range of pollutants,thereby affecting the local pollutant concentration.Inversion occurred frequently during heavy pollution,and the surface layer inversion mainly occurred at night and early morning,with the inversion intensity reaching 3℃/(100 m).The pollutants accumulated in the lower layer of inversion and beaneath it.

Abstract:Zhang Peichang,Professor of Information Science and Technology at Nanjing University,is a well-known expert in Radar Meteorology,and one of the few key participants and initiators in the development and construction of China's weather radar CINRAD network system.Prof.Zhang has published 106 articles according to the preliminary collection,all of which are associated with topics of interest in Radar Meteorology,such as weather radar networking and image mosaic,qualitative precipitation estimation,radar equation for meteorology and attenuation correction,retrievals from radar observations,atmospheric refraction and radar data quality control for ground clutters,and precipitable particles' features in microwave bands.This paper summarizes the task we have completed for processing and classification on the collected particles,and includes a review on the features of the collected particles in terms of chronology,content taxonomy,and co-authors.It is our hope that accomplishing this task will promote the early publication of Selected Collection of Zhang Peichang's Works in Radar Meteorology.We believe that this anthology will be conducive to understanding Prof. Zhang's contributions to developing Chinese weather radar systems and radar meteorology,as well as to learning from him so that we may make our own contributions to this field.